"There are no additional details at this time. Information will be released as it is available."

A later tweet added: "Our first priority in any emergency incident is to protect the men and women at Wright-Patt. Our base security forces defenders and fire department personnel are trained to quickly assess situations and take necessary action.

"An investigation is under way."

US TV station WDTN reports that the man has barricaded himself on the fourth floor of the base hospital.

DAYTON DAILY NEWS

BREAKING There is an active shooter at a major US air force base

News agency AP reported the Ohio State Highway Patrol and local police were sending personnel to the base.

A loudspeaker announced that base was on lock down.

WHIO-TV reported that an announcement was made at the medical centre telling some people inside the building to leave with their hands on their heads.

Robert Jones Portman the junior United States Senator for Ohio, tweeted: "Jane and I are following the events unfolding at Wright-Patt. We thank our first responders for their efforts & are praying for a safe conclusion for everyone involved."

An employee at Wright-Patterson Air Force base later told FOX45 the all-clear has been give.

GETTY

MILITARY: Wright-Patterson is one of the largest bases in the US. File picture

Twitter user @lexalcocer tweeted: "If everyone could say a prayer for my cousin Brooke. There’s an active shooter on the hospital where she works on base at Wright Patterson Air Force Base."